Mumford was born in New London, Connecticut on January 29, 1764,[1] and named in honor of his maternal grandfather.
Envoy to France Silas Deane (the husband of his mother's younger sister, Elizabeth Saltonstall),[2] he was a private secretary to Benjamin Franklin during the latter part of his official residence in Paris.
In 1805, he was elected as a Democratic-Republican to the Ninth Congress to fill the vacancy caused by the resignation of Representative-elect Daniel D. Tompkins.
[1] After retiring from active political life, he was elected director of the Bank of New York in 1812, and opened a broker's office in Wall Street in 1813.
Together, they lived at 23 Broadway and were the parents of:[2] He died from a lingering illness in New York City on Saturday, April 30, 1831 and was interred in the Old Collegiate Dutch Church Cemetery.